1. Field of the Invention
This invention provides a process for the alkylation of olefins with alkanes having at least one tertiary carbon atom, i.e., an isoalkane, in the presence of a catalyst complex comprising an organosulfonic acid having at least one covalent carbon-fluorine bond or one carbon-phosphorus bond provided by a phosphono radical and a Lewis acid to yield an alkylate reaction product useful for adding to gasoline to improve the octane rating.
2. Background of the Invention
The preparation of high octane blending components for motor fuels using strong acid alkylation processes (notably where the acid is hydrofluoric acid or sulfuric acid) is well known. Alkylation is the reaction in which an alkyl group is added to an organic molecule, typically an aromatic or olefin. For production of gasoline blending stocks, the reaction is between an isoparaffin and an olefin. Alkylation processes have been in wide use since World War II when high octane gasolines were needed to satisfy demands from high compression ratio or supercharged aircraft engines. The early alkylation units were built in conjunction with fluid catalytic cracking units to take advantage of the light end byp-roducts of the cracking units: isoparaffins and olefins. Fluidized catalytic cracking units still constitute the major source of feedstocks for gasoline alkylation units. In spite of the mature state of strong acid alkylation technology, existing problems with the hydrofluoric and sulfuric acid technologies continue to be severe: disposal of the used acid, unintentional emission of the acids during use or storage, substantial corrosivity of the acid catalyst systems, and other environmental concerns.
Although a practical alkylation process using solid acid catalysts having little or no corrosive components has long been a goal, commercially viable processes do not exist.
The open literature shows several systems used to alkylate various hydrocarbon feedstocks.
The American Oil Company obtained a series of patents in the mid-1950s on alkylation processes involving C.sub.2 -C.sub.12 (preferably C.sub.2 or C.sub.3) olefins and C.sub.4 -C.sub.8 isoparaffins. The catalysts used were BF.sub.3 -treated solids and the catalyst system (as used in the alkylation process) also contained free BF.sub.3.
Other references later suggested the use of Lewis acids to modify solid catalysts for use in alkylation processes.
For example, U.S. Pat. No. 3,068,301 to Hervert et al. suggests a catalyst for alkylating aromatics using "olefin-acting compounds". The catalyst is a solid, silica-stabilized alumina, comprising up to 10% SiO.sub.2, all of which has been modified with up to 100% of weight BF.sub.3.
In U.S. Pat. No. 4,407,731 to Imai, a high surface area metal oxide such as alumina (particularly gamma-alumina, eta-alumina, theta-alumina, silica, or a silica-alumina) is used as a base or support for BF.sub.3. The BF.sub.3 treated metal oxide is used for generic oligomerization and alkylation reactions.
Similarly, U.S. Pat. No. 4,427,791 to Miale et al. suggests the enhancement of the acid catalytic activity of inorganic oxide materials (such as alumina or gallia) by treating the material with ammonium fluoride or boron fluoride, contacting the treated inorganic oxide with an aqueous ammonium hydroxide or salt solution, and calcining the resulting material. The inorganic oxides treated in this way are said to exhibit enhanced Bronsted acidity and therefore are said to have improved acid activity towards the catalysis of numerous and several reactions (such as alkylation and isomerization of various hydrocarbon compounds).
U.S. Pat. No. 4,751,341 to Rodewald shows a process for treating a ZSM-5 type zeolite with BF.sub.3 to reduce its pore size, enhance its shape selectivity, and increase its activity towards the reaction of oligomerizing olefins. The patent also suggests using these materials for alkylation of aromatic compounds.
Certain Soviet publications suggest the use of Al.sub.2 O.sub.3 catalysts for alkylation processes. Benzene alkylation using those catalysts (with 3 ppm to 5 ppm water and periodic additions of BF.sub.3) is shown in Yagubov, Kh. M. et al., Azerb. Khim. Zh., 1984, (5) p. 58. Similarly, Kozorezov, Yu and Levitskii, E. A., Zh. Print. Khim. (Leningrad), 1984, 57 (12), p. 2681, show the use of alumina which has been treated at relatively high temperatures and modified with BF.sub.3 at 100.degree. C. Isobutane alkylation using Al.sub.2 O.sub.3 /BF.sub.3 catalysts is suggested in Neftekhimiya, 1977, 17 (3), p. 396; 1979, 19 (3), p. 385. The olefin is ethylene.
U.S. Pat. No. 4,918,255 to Chou et al. suggests a process for the alkylation of isoparaffins and olefins using a composite described as "comprising a Lewis acid and a large pore zeolite and/or a non-zeolitic inorganic oxide". The process disclosed requires isomerization of the olefin feed to reduce substantially the content of alpha-olefin and further suggests that water addition to the alkylation process improves the operation of the process. The best Research Octane Number (RON) product made using the inorganic oxides (in particular SiO.sub.2) is shown in Table 6 to be 94.0.
Similarly, PCT published applications WO 90/00533 and 90/00534 (which are based in part on the U.S. patent to Chou et al. noted above) suggest the same process as does Chou et al. WO 90/00534 is specific to a process using boron trifluoride-treated inorganic oxides including "alumina, silica, boria, oxides of phosphorus, titanium oxide, zirconium oxide, chromia, zinc oxide, magnesia, calcium oxide, silica-alumina-zirconia, chromia-alumina, alumina-boria, silica-zirconia, and the various naturally occurring inorganic oxides of various states of purity such as bauxite, clay and diatomaceous earth". Of special note is the statement that the "preferred inorganic oxides are amorphous silicon dioxide and aluminum oxide". The examples show the use of amorphous silica (and BF.sub.3) to produce alkylates having an RON of no greater than 94.
Certain references have suggested that sulfonic acid-containing polymers may be used as catalysts in alkylation processes. One series of such sulfonic acid-containing polymers comprises polymers having an organic backbone, e.g., a polystyrene sulfonic acid polymer. For example, see U.S. Pat. Nos. 3,855,342; 3,855,343; and 3,862,258. Another series of such sulfonic acid-containing polymers comprises polymers having an inorganic backbone derived by reacting a pentavalent atom-containing acid, e.g., phosphonic acid or a phosphinic acid, with a tetravalent metal salt to yield a polymer having an inorganic backbone. These inorganic polymers are taught in U.S. Pat. Nos. 4,232,146; 4,235,990; 4,235,991; 4,256,872; 4,267,308; 4,276,409; 4,276,410; 4,276,411; 4,298,723; 4,299,943; 4,373,079; 4,384,981; 4,386,013, 4,390,690; 4,429,111; and 4,436,899. The use of sulfonic acid containing derivatives of such inorganic polymers is taught in U.S. Pat. No. 4,868,343, wherein it is disclosed that the pentavalent atom-containing acid may include a sulfonic acid group or a sulfonatable radical such as an aromatic or olefinic radical which is sulfonated after the formation of the inorganic polymer to yield an inorganic polymer having pendant sulfonic acid radicals.
Finally, see PCT published application WO 90/07480, which discloses the use of fluorinated phosphono sulfonic acids, alone, or reacted with a tetravalent metal ion, as above, as catalysts for the alkylation of aromatics with olefins.